The present disclosure relates to a distance measuring device comprising at least one distance measuring unit, in particular for a contactless distance measurement, which has at least one transmission device for emitting reference and measurement radiation and a sensor device for detecting reference and measurement radiation.
Distance measuring instruments, in particular optical distance measuring instruments, which emit a time-modulated beam, in particular a light beam, in the direction of a target object, the distance of which from the measuring instrument is intended to be established, are known. A returning beam, in particular light beam, reflected or scattered by the targeted target object is at least partly detected by the instrument and used for establishing the distance to be measured. A typical measurement range in this case lies in a distance range from a few centimeters to several hundred meters. The established distance measurement value is subsequently output to the user on an output device, for example in the form of a display.
In order to obtain a high measurement accuracy using such an instrument, the instruments typically have an instrument-internal reference section with a known length, via which the transmission radiation can be guided directly onto a reception apparatus of the measuring instrument, e.g. a detector. The internal reference section serves for calibrating the measurement instrument and, in particular, for taking into account short-term drifts of the components of the device for the distance measurement, as occur, for example, as a consequence of temperature variations or mechanical tensions.
DE 102 004 023 998 A1 has disclosed a device for optical distance measurement, in which there are                a transmission branch defining a transmission channel, which has at least one transmission unit for emitting modulated, optical transmission radiation in the direction of the target object,        a reception branch defining a reception channel, comprising at least one reception apparatus for receiving reception radiation, and        a reference branch defining a reference section.        
Mechanically operated switching means in the form of adjustable reflecting flaps allow temporary redirection of the transmission radiation between the transmission branch and the reference branch such that the transmission radiation is redirected within the instrument and directed onto a photodiode via a reference section with a known length.